trunkmunki Senior Heliman Location: Bangor
| "In modern high speed gasoline engines, exhaust valves and the surfaces they rest on (the valve seats) operate at high temperatures and with severe mechanical stresses. Under conditions of high speed, and to a lesser extent high load, and in the absence of special protection of the valve seat, it has been found that the material of the valve seat can be eroded away, i.e. “recede” into the cylinder head. In the extreme, this can cause lower compression, poor fuel economy, high emissions and mechanical problems. Lead compounds formed by the combustion of lead anti knock additives prevent valve seat recession by forming a thin non metallic layer of lead oxides and sulfates on the surface of the seat. This acts as a lubricant, preventing metal - metal contact and welding which causes valve seat recession."
Source: ”Prevention of Valve-Seat Recession in European Markets”, McArragher, Clark & Paesler, CEC/93/EF19, May 1993. |